1. Field of the Invention
The present invention relates to a navigation apparatus and an intersection-guidance method. More particularly, the present invention relates to a navigation apparatus and an intersection-guidance method for displaying a guidance route on a map and for displaying an enlarged view of an intersection on the guidance route for indicating the direction in which a vehicle should travel at the intersection when the vehicle approaches the intersection.
2. Description of the Related Art
In the past, a navigation apparatus detects the position of a vehicle and reads map data for the area around the vehicle position from a map-information recording medium such as a CD-ROM, a DVD, and so forth. Then, the navigation apparatus draws and displays a map image on a display-screen and draws and displays a mark indicating the vehicle at a predetermined position on the map image. As the vehicle travels, the navigation apparatus changes the position of the vehicle mark according to the change in the current position of the vehicle. In another case, the vehicle mark is fixed at a predetermined position on the display-screen, such as the center. Then, by scrolling the map image, it becomes possible to easily understand the map data for the area around the vehicle position at all times. Such a navigation apparatus has a route-guidance function. Therefore, the navigation apparatus can search for a route that leads from a start-point to a destination in the shortest time or by the shortest distance, and can display such a route on the display screen for guiding the driver of the vehicle to the destination. With the route-guidance function, when the vehicle approaches an intersection, an enlarged view of the intersection is displayed for indicating the direction in which the vehicle should travel at the intersection. Further, voice guidance is used for informing the driver of the travel direction to prevent the driver from going in the wrong direction at the intersection.
In the past, the enlarged view of the intersection is generated with reference to a road attribute that is stored in a map database for informing the driver of the traveling direction. However, such a road attribute does not include attributes of an intersection with a peculiar shape such as that shown in FIG. 9A, which is a Spanish left-turn intersection which is common in Latin countries such as Spain, Portugal, and so forth. Also, the road attribute does not include attributes of an intersection with a peculiar shape such as that shown in FIG. 10A, which is a Michigan left-turn intersection commonly found in the State of Michigan, U.S.A.
According to the road attribute of the Spanish left-turn intersection in FIG. 9A, the vehicle turns right at a branch intersection BRC before a no-left-turn intersection LTIC and enters the no-left-turn intersection LTIC as shown by a guidance route IRD. In this manner, the vehicle effectively can turn left at the no-left-turn intersection LTIC.
According to the road attribute of the Michigan left-turn intersection in FIG. 10A, the vehicle turns right at a branch intersection BRC before a no-left-turn intersection LTIC, turns left at a road RD, and travels straight ahead at the no-left-turn intersection LTIC, as shown by a guidance route IRD. In this manner, the vehicle effectively can turn left at the no-left-turn intersection LTIC.
Usually, existing map databases such as the above-described map database give an indescribable-attribute (an attribute that is untrustworthy or unreliable) to a turning link LK (indicated by arrow GA) of the Spanish left-turn intersection. However, it is unclear whether or not all the intersections have such an attribute. Further, the Spanish left-turn is not clearly defined in the specifications of such map databases. Therefore, two kinds of maneuver displays, that is, MN1 and MN2 shown in FIG. 9B are shown on one screen for illustrating the enlarged view of the Spanish left-turn intersection. MN1 shows an arrow pointing in a direction for guiding the vehicle to turn obliquely right. On the other hand, MN2 shows an arrow pointing in a direction for guiding the vehicle to turn obliquely left. In the case of the Michigan left-turn intersection, two kinds of maneuver displays, that is, MN1xe2x80x2 and MN2xe2x80x2 shown in FIG. 10B are shown on one screen for illustrating the enlarged view of the Michigan left-turn intersection. MN1xe2x80x2 shows an arrow pointing in a direction for guiding the vehicle to turn obliquely right. MN2xe2x80x2 shows an arrow pointing in a direction for guiding the vehicle to turn left. In each of FIGS. 9B and 10B, the two maneuver displays are shown on one screen. This is because the distance between the intersections is short (less than 150 meters). If the distance is 150 meters or more, the two maneuver displays are shown on separate screens in order.
Thus, in the past, when the driver is close to the Spanish left-turn intersection or the Michigan left-turn intersection, the driver is first guided to turn right at the intersection by the enlarged view of the intersection where the driver should be guided to turn left. Therefore, the driver is confused by such guidance.
Accordingly, it is an object of the present invention to display an enlarged view of an intersection appropriately without confusing a driver when the road attribute of the intersection is a Spanish left-turn or a Michigan left-turn.
According to an intersection-guidance method of the present invention, monitoring is performed to determine whether or not the vehicle is close to a first point in a road where the vehicle turns right before a no-left-turn intersection for entering and turning left at the no-left-turn intersection. When the vehicle is close to the first point in the road, the direction in which the vehicle should travel from the first point in the road to a second point beyond the no-left-turn intersection is continuously indicated by an arrow in one enlarged view of the intersection. Subsequently, the display of the enlarged view of the intersection can be shown appropriately without confusing the driver when the road attribute of the intersection is a Spanish left-turn or a Michigan left-turn. That is to say, because the driver is informed of the correct path in which he/she should travel, he/she is prevented from going in a wrong direction.
Preferably, the first point in the road is a start-point node of two or more exit links when an end-point node of at least one of the exit links not forming the guidance route exists on the guidance route. For showing a display of an enlarged view of an intersection that can be used for either a Spanish left-turn intersection or a Michigan left-turn intersection, a vehicle approaching the first point in the road (a branch intersection) may be detected. Then, the direction in which the vehicle should travel from the first point in the road to a second point beyond the no-left-turn intersection may be continuously indicated by an arrow in one enlarged view of the intersection. Subsequently, the display of the enlarged view of the intersection can be shown appropriately without confusing the driver.
Preferably, the first point in the road is a start-point node of two or more exit links when two of the exit links have the same end-point node and when one of the two exit links forms the guidance route. For showing a display of an enlarged view of an intersection that can be used for a Spanish left-turn intersection, a vehicle approaching the first point in the road (a branch intersection) may be detected. Then, the direction in which the vehicle should travel from the first point in the road to the second point beyond the no-left-turn intersection may be continuously indicated by an arrow in one enlarged view of the intersection. Subsequently, the display of the enlarged view of the intersection can be shown appropriately without confusing the driver.
Preferably, the first point in the road is a start-point node of two or more exit links when an end-point node of at least one of the exit links not forming the guidance route exists on the guidance route and when the guidance route passes through the end-point node in a straight line. For performing a display of an enlarged view of an intersection that can be used for a Michigan left-turn intersection, a vehicle approaching the first point in the road (a branch intersection) may be detected. Then, the direction in which the vehicle should travel from the first point in the road to the second point beyond the no-left-turn intersection may be continuously indicated by an arrow in one enlarged view of the intersection. Subsequently, the display of the enlarged view of the intersection can be shown appropriately without confusing the driver.